1. Field of the Invention
The present invention relates generally to a thawing or defrosting apparatus and, more particularly, to a defrosting apparatus capable of defrosting frozen articles such as frozen foods without incurring an undesired temperature rise thereof which would adversely influence such foods.
2. Description of the Prior Art
There have heretofore been known defrosting apparatuses such as a defroster box and a combined defrosting and refrigerating box for defrosting frozen foods or the like such as fresh-meat, fish, shell fish, vegetables, fruits etc. In the defrosting operation of the hitherto known defrosting apparatus, it has been observed that when a defrosting heater is electrically energized continuously for effectuating the defrosting operation, some of the foods are subjected to adverse influences such as by degradations in quality due to an excessive rise in temperature upon completion of defrosting of all the foods. Under such circumstances, a control has been adopted in which a temperature range is so set that the temperature of the hot air discharged from an air circulation fan is allowed to vary within a preset temperature range, wherein the defrosting heater is turned on and off at temperature levels corresponding to the respective lower and upper limits of the temperature range so that the temperature of the outlet air discharged from the circulation fan will not be increased excessively. This is however disadvantageous in that consistent control of the amount of time required for the defrosting can not be realized since identical defrosting completion temperatures can not always be detected because the temperature of the inlet air drawn in by the air circulation fan is not stable. Furthermore, in the case of combined defrosting and refrigerating apparatuses in general, the defrosting operation is controlled by detecting the defrosting start temperature (i.e. the temperature at which the defrosting operation is to be started) and the defrosting completion temperature (i.e. the temperature at which the defrosting operation is to be completed), while the refrigerating operation is controlled by detecting preset lower and upper limits of the interior temperature (also referred to as intra-box temperature). However, in view of the fact that the temperature range set for the control of the defrosting operation differs from that set for the refrigerating operation control, it is necessary to provide two temperature sensors or thermostats, one for the former and the other for the latter. Besides, in the case of the defroster, there is another disadvantage in that when the interior temperature is higher than the defrosting start temperature, the defrosting start switch is not allowed to be closed until the interior temperature has been lowered to the defrosting start temperature.